RE: [PATCH v1 1/2] scsi: ufs: set device as default active power mode during initialization only

From: Avri Altman <Avri.Altman@wdc.com>
To: Stanley Chu <stanley.chu@mediatek.com>, Can Guo <cang@codeaurora.org>
Cc: "martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
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	"kuohong.wang@mediatek.com" <kuohong.wang@mediatek.com>,
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Subject: RE: [PATCH v1 1/2] scsi: ufs: set device as default active power mode during initialization only
Date: Sun, 5 Jan 2020 07:55:25 +0000	[thread overview]
Message-ID: <MN2PR04MB69913BBFD9DF5268894C94A9FC3D0@MN2PR04MB6991.namprd04.prod.outlook.com> (raw)
In-Reply-To: <1577947124.13164.75.camel@mtkswgap22>

Hi Stanley,
I am aware that this discussion is already concluded,
Just pointing out a small issue that might ease your mind further.

Thanks,
Avri

> 
> Hi Can,
> 
> On Tue, 2019-12-31 at 16:35 +0800, Can Guo wrote:
> 
> > Hi Stanley,
> >
> > I missed this mail before I hit send. In current code, as per my
> > understanding, UFS device's power state should be Active after
> > ufshcd_link_startup() returns.
> > If I am wrong, please feel free to correct me.
> >
> 
> Yes, this assumption of ufshcd_probe_hba() is true so I will drop this patch.
> Thanks for remind.
> 
> > Due to you are almost trying to revert commit 7caf489b99a42a, I am
> > just wondering if you encounter failure/error caused by it.
> 
> Yes, we actually have some doubts from the commit message of "scsi: ufs:
> issue link startup 2 times if device isn't active"
> 
> If we configured system suspend as device=PowerDown/Link=LinkDown mode,
> during resume, the 1st link startup will be successful, and after that device could
> be accessed normally so it shall be already in Active power mode. We did not
> find devices which need twice linkup for normal work.
> 
> And because the 1st linkup is OK, the forced 2nd linkup by commit "scsi:
> ufs: issue link startup 2 times if device isn't active" leads to link lost and finally
> the 3rd linkup is made again by retry mechanism in
> ufshcd_link_startup() and be successful. So a linkup performance issue is
> introduced here: We actually need one-time linkup only but finally got 3 linkup
> operations.
> 
> According to the UFS spec, all reset types (including POR and Host UniPro Warm
> Reset which both may happen in above configurations) other than LU reset, UFS
> device power mode shall return to Sleep mode or Active mode depending on
> bInitPowerMode, by default, it's Active mode.
As for bInitPowerMode - please see the discussion in https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg78262.html

> 
> So we are curious that why enforcing twice linkup is necessary here?
> Could you kindly help us clarify this?
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